Molecular Population Genetics Of Wheat Dwarf Virus (WDV) And Barley Yellow Dwarf Viruses (BYDVs)-PAVs

Wheat dwarf virus (WDV), transmitted by leafhopper (Psammotettix striatus L.), is a member of the genus Mastrevirus, Geminiviridae. In2007, its occurrence was reported firstly in China by our laboratory, and then it epidemic extensively in Hancheng, Shaanxi in2007and2008, caused severe loss for wheat yield. Because the great differences in environment and geography in cereal regions of China, the population of WDV should be abundant variety. The experiments detecting WDV on the wheat and barley from different regions with PCR and ELISA were developed and abroad distribution and evolution of the WDV in our country.Based on the genome sequence of WDV on GenBank, three pair of special primers was designed. The expected special three segments with overlapping regions were obtained by PCR, and then cloned into the plasmid and sequenced. The full genome sequences of90WDV isolates were obtained, in which84isolates collected from wheat and6isolates from barley in the northwest, southwest, centeral and north of China.From the the robust phylogenetic tree, it was concluded as the followings.(1) The isolates were clustered into three subpopulations according to their hosts, i.e. barley, oat and wheat subpopulation respectively in which the evolution of WDV hosted on oat was independent. In the clade of WDV on wheat, it was devided into two sub-groups of Chinese and other countrys, but the Sweden wheat isolates were basal to those from China. In the clade of barley isolates, all isolates were collected from foreign countryt. In our research, the genomonic sequences of7barley isolates from Kunming, Yunnan were obtained, but they showed a high nucleotide identities (98.0%-99.6%) with wheat isolates and a very low identities (83.4%-83.7%) with barley isolates reported in other countrys. It suggested that the species of WDV on wheat could infect barley plants. However, it was necessary to focus further on the biological validation.(2) In the clade of WDV on wheat, the Chinese isolates were obviously different from foreign wheat isolates. However, the Chinese wheat isolates were not clustered by geographical orgins or collection times, while the foreign wheat isolates were clearly clustered by the geographical orgins with a few of exceptions.(3) The isolates from Tianshui and Jining were concentrative distribution in the phylogenetic tree, while the isolates from Hancheng, Shijiazhuang, and Kunming had abundant diversification because they dispersedly scattered in different groups in the phylogenetic tree.From the analysis of levels and patterns of intraspecific polymorphism and selective constraints of WDV genes, the population of WDV was being a expand progress and the positive selection in the evolutionary process. The Rep A gene was most unstable, then the Rep gene was in order, all of the characteristics of molecular variability was being for the changes of environment and hosts.Barley yellow dwarf viruses (BYDVs), transmitted naturally by at least25aphid species in a highly specific, circulative, non-propagative manner, are a kind of+ssRNA viruses. Plant RNA viruses provided promising new avenues for experimental evolution based on the dynamics of adaptation, genetic diversification and the evolution of mutational robustness. This research collected the full genomic sequences of58BYDV-PAVs including30isolates collected from different regions of China and sequenced in our laboratory, to analyze the molecular population genetics, orgins and evolution of BYDV-PAV population. The results could help us to understang the interaction between wheat and virus, the epdimcic trendency and the control basis of the disease.The phylogenetic analysis and molecular population diversity of58BYDV-PAV isolates described the evolution relationship among the isolates from worldwide including China, the seven subgroups were found in the phylogenetic tree, the Chinese isolates focused in five subgroups, in which three subgroups consisted entirely with the Chinese isolates. The isolates in other two subgroups mainly came from China, USA, Japan and Australia. From the phylogenetic tree, the Chinese isolates distinctly showed that genus Luteovirus (BYDV-PAV, GAV and MAV) ironically has more features in common with the Tombusviridae family than it does with the Luteoviridae. Moreover, in the clades of BYDV-PAVs, the Chinese isolates were more obviously different from the isolates from foreign other countrise. However, the Chinese isolates were not clustered by geographical orgins, different hosts or collection times, while the foreign wheat isolates were clearly clustered by the geographical source except some scattered isolates.According to the recent ruling that a difference at the amino acid level exceeding10%for any viral gene product could be used as the sole criteria to discriminate between species within the Luteoviridae, the BYDV-PAVs could be classified into five different species, i.e. PAV-â… , PAV-â…¡, PAV-â…¢, PAV-â…£ and PAV-â…¤ respectively. The three new species existing only in China further reflected the robust diversification in the natural population of China. In the coding regions, MP gene possessed the same amino acid substitution model with the HIV-1, and had the most positively selected sites. BYDV-PAV exhibited a relatively high frequency of homologous recombination especially between the Chinese isolates and other countries'isolates mainly in RdRp, CP and HC-Pro, which suggested the population of BYDV-PAV would have more multifarious diversity.